The present invention relates to a liquid crystalline polyester and a method for producing thereof.
Liquid crystalline polyesters are useful as thermoplastic resins excellent in heat resistance. Especially, a liquid crystalline polyester composed of 4-hydroxybenzoic acid and 2-hydroxy-6-naphthoic acid has been widely used primarily in the electrical and electric field.
Japanese Patent Laid-Open No. 54-77691 discloses a liquid crystalline polyester obtained by polymerizing p-acetoxybenzoic acid and 2-acetoxy-6-naphthoic acid at 250-320xc2x0 C. However, the fluidity of the obtained liquid crystalline polyester is insufficient in thin-walled portions when a thin-walled article is molded, and the mechanical strengths such as the tensile strength of the molded article obtained is not sufficient.
Further, a liquid crystalline polyester composed of four units derived from 4-hydroxybenzoic acid, 2-hydroxy-6-naphthoic acid, 4,4xe2x80x2-dihydroxybiphenyl and terephthalic acid has been widely used primarily in the electrical and electric field. However, such liquid crystalline polyester has the same problem as above.
As products have been made thinner and smaller in recent electrical and electric fields, there has been required the development of a liquid crystalline polyester that can be used in production of a molded article having sufficient mechanical strengths in which the melted liquid crystalline polyester has sufficient fluidity in thin-walled portions when the thin-walled molded article is manufactured.
The object of the present invention is to provide a liquid crystalline polyester that can be used in production of a molded article having sufficient mechanical strengths in which the melted liquid crystalline polyester has sufficient fluidity in thin-walled portions when the thin-walled molded article is manufactured, and to provide a method for producing the liquid crystalline polyester.
The present inventors carried out studies earnestly to find a liquid crystalline polyester and a method for production thereof without the above problems, and the inventors found out that a liquid crystalline polyester obtained by copolymerizing 4-acyloxybenzoic acids (I) and 2-acyloxy-6-naphthoic acids (II) in the presence of an imidazole (V) can be used in production of a molded article in which the melted liquid crystalline polyester has sufficient fluidity in thin-walled portions when the thin-walled molded article is manufactured, and which has sufficient mechanical strengths as well, thereby completing the present invention.
The present inventors also found that a liquid crystalline polyester obtained by copolymerizing 4-acyloxybenzoic acids (I), 2-acyloxy-6-naphthoic acids (II), 4,4xe2x80x2-diacyloxybiphenyls (III) and phthalic acids (IV) in the presence of an imidazole (V) can be used in production of a molded article in which the melted liquid crystalline polyester has sufficient fluidity in thin-walled portions when the thin-walled molded article is manufactured, and which has sufficient mechanical strengths as well, thereby completing the present invention.
That is, the present invention provides a liquid crystalline polyester obtained by copolymerizing a 4-acyloxybenzoic acid of Formula (I): 
(wherein R1 represents an alkyl group of 1 to 5 carbon atoms), and a 2-acyloxy-6-naphthoic acid of Formula (II): 
(wherein R2 is an alkyl group of 1 to 5 carbon atoms), in the presence of imidazoles of Formula (V): 
(wherein X1 to X4 represent a hydrogen atom, or each independently represents an alkyl group, hydroxymethyl group, cyanoalkyl group, carboxyl group, aminoalkyl group, phenyl group, benzyl group or formyl group.).
The present invention also provides a liquid crystalline polyester obtained by copolymerizing above 4-acyloxybenzoic acid of the above Formula (I), 2-acyloxy-6-naphthoic acid of the above Formula (II), a 4,4xe2x80x2-diacyloxybiphenyls of Formula (III): 
(wherein R3 and R4 represent independently alkyl groups of 1 to 5 carbon atoms),
and a phthalic acid of Formula (IV): 
in the presence of imidazoles of the above Formula (V).